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Need to breathe
Monitoring soil oxygen levels for success.
Editor’s note: This story previously appeared in the August 2006 issue
of GreenMaster, the official publication of the The Canadian Golf
Superintendent Association.
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Iron exit vents are easy to locate and excellent for monitoring that drains are flowing and not backed up once greens mix reaches field capacity. Photos courtesy of Cordova Bay GC |
During my 20 years as a superintendent, I have faithfully taken soil tests to monitor the chemical and nutritional values of soil on greens, tees and fairways. While this information is critical in making sound management decisions on fertility programs, I recently learned I was overlooking the most important factor in developing management programs for promoting strong, healthy turf.
A couple of years ago, I attended a seminar by Dave Doherty from the International Sports Turf Research Center (ISTRC) on soil physical properties. He discussed several concepts that will forever change the way I manage greens. Doherty emphasized how important gas exchange and oxygen are in the profile, and he showed how monitoring the physical properties of soil profiles with regular testing would help me make informed decisions when developing management programs. In a nutshell, through Doherty’s observations at hundreds of golf courses across North America, he was able to identify the soil physical properties common to greens that are easy to maintain and to greens that fail or are very difficult to manage.
Benchmark testing: the first report card
The ISTRC lab, based in Olathe, Kan., provides two sets of data. The first set consists of physical evaluation, the evaluation of the root systems and the measurement of the organic matter in each 1-inch (25.4-millimeter) increment to a depth of 4 inches (101.6 millimeters). The second set of data contains the textural and particle-size analysis. The combination of these data provides information on the greens’ infiltration rate in millimeters per hour, subsurface air capacity (noncapillary porosity), water porosity (capillary porosity), bulk density and percentage of organic matter. The data this testing provides will help monitor the aging process of the putting surface root zones, while also evaluating the effectiveness of current cultural practices. A well-built green is designed to provide a profile with 60 percent solids, 20 percent air-pore space and 20 percent water-pore space. These values can provide the correct environment for a strong root zone and healthy turf. As greens age, these values tend to shift dramatically if cultural programs are not designed to maintain original conditions through the removal of organic matter and the addition of sand topdressing to dilute the organic matter produced by the plant’s life cycle.
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I have found the information provided by the physical property soil tests invaluable when making management decisions regarding the necessary cultural programs for upcoming seasons at my facility — Cordova Bay Golf in Victoria, British Columbia. The data provided can also help illustrate to our employers that we superintendents have developed our cultural programs based on sound facts. In addition, such scheduled procedures are necessary for the long-term benefits of the course’s putting surfaces.
Selecting tine size and spacing
Once the physical properties of your existing greens have been tested and determined, the necessary aeration schedule can be easily outlined. To help identify ideal physical properties, the ISTRC established values for superintendents to work toward (see chart above). We tested our No. 1 green and came up with the following values (see chart, Page 76).
Using these results, ISTRC agronomists recommended we develop a program for this season to displace 25 percent of the putting surface using the aeration tines’ outer diameter in the calculation. Using the ISTRC’s surface-area calculator, we can insert different spacing and tine sizing to come up with the best tine to achieve certain goals.
Many golf courses are switching to carbide-tipped aeration tines for longevity, which is probably a good idea. During our most recent aeration, we used a standard side-eject quad tine, and because they were not carbide-tipped, the tines were changed after every 20,000 square feet (1,858 square meters) of aeration, or roughly every three greens. Halfway through the aeration of our 12th green, the tines were changed, and we noticed the removed core was significantly different.
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Left: Poor soil conditions and the presence of black layer before ventilation of greens’ drainage. Right: Root-zone soil conditions improved dramatically with greens’ drainage ventilation. Photos courtesy of ISTRC |
The difference in the core pulled from a new aeration tine and one that has been worn down by 0.33 inch (8.3 millimeters) in length is significant. When the tine is new, 3.75 percent of the green is removed using the inner diameter and 10.04 percent is removed calculating with the outer diameter dimension of the tine. After 20,000 square feet (1,858 square meters), the same tine has been worn down by 0.25 inch (6.35 millimeters), but the inner diameter and outer diameter dimensions of the tine have changed, resulting in 6.24 percent removal using the inner diameter in the calculation and 9.01 percent using the outer diameter dimension.
These data suggest that it is important to change standard aeration tines more frequently or rotate in the order in which the greens are aerated each season. The purpose of this technique is to ensure that the amount of material moved from each green during the season is similar. Using soil tests to monitor the changing physical properties of the greens is a useful tool in management programs.
Root-zone oxygen and harmful gases
Several factors affect the oxygen levels in soils, and core aeration is only the first step in maintaining high oxygen levels. Aeration is the venting of soil, which enables gases to move in and out of the soil profile. High water content in soils causes oxygen deficiency in roots because water-filled pores block the diffusion of oxygen into the soil to replace those used by respiration. In fact, according to Nyle Brady and Ray Weil, authors of “The Nature and Properties of Soils,” oxygen diffuses 10,000 times faster through a pore filled with air than through a similar pore filled with water. Once soil temperatures warm up and we approach the growing season, oxygen can be depleted rapidly through consumption by actively growing turf roots or by soil microbes that are decomposing readily available supplies of organic matter. If organic matter decomposes under low-oxygen soil conditions, then gases such as methane (CH4), hydrogen sulfide (H2S) and ethylene (C2H4) are produced. Therefore, during the growing season when microbes are very active, it is essential your management programs focus on the constant addition of oxygen in a variety of methods to encourage the decomposition of organic matter and allow for adequate displacement of any harmful gases that may form during these processes. I believe the following tools and procedures are of primary importance for a solid Integrated Pest Management (IPM) program:
• Hydroject. During the growing season, when more disruptive methods are unacceptable, this tool may become a superintendent’s best friend in terms of managing gas exchange in the soil profile.
• Planet Aire. This tool is gaining popularity because of the ease and speed at which aeration can occur. With this machine, nondisruptive aeration can be performed on greens in as little as four hours.
• Spiking with a 0.25-inch (6.35-millimeter) solid tine. This procedure creates excellent chimneys for gas exchange to take place, and it causes minimal surface disruption when combined with light topdressing.
Proper greens drainage and venting: an important piece of the puzzle
Once a program is implemented to monitor and manage the air-pore space in the greens, it is critical to ensure the drainage systems installed in your greens during construction are functioning and properly venting. This will allow oxygen flow into the root zone as well as the flushing of the harmful gases created by microbial activity and by the plant during respiration that is consuming oxygen and producing carbon dioxide. In order for this to occur, cleanouts or blowouts need to be installed at the upper end of each drain tile loop, and air vents need to be installed where each drain line exits the green (see photo, Page 74). Today, most golf courses are being designed with blowouts and vents installed during construction. However, most older courses did not include this important specification in the construction plans. If certain greens have proven to be a challenge in the past, it may be helpful to locate the drains exiting the greens and flush them to ensure the tiles are open and functioning well.
The concept of venting is best described by comparing greens to a basement. Envision a basement with several people living in it with no windows or doors to properly vent the room. It would not take long for uninhabitable conditions to develop and inadequate oxygen levels to exist because the inhabitants would consume the oxygen and harmful gases would build up. If you took this same basement and installed a window at each end to allow proper aeration and venting, the room would become much more habitable and those living in the space would be much healthier as a result. The same holds true with your greens — by installing vents at either end, fresh oxygen can be drawn down into the greens table, and the water will flow more freely through the tiles.
Troubled greens: you will be amazed by what you find
Recently we completed the process of venting our greens and exposed several causes of the problems we have been experiencing over the years. Our eighth green has been difficult to manage, even though it is one of the largest on the golf course and is fully exposed to the sun. When we located the drain exiting the back of the green, we found the tile had been cut during the installation of the irrigation system 16 years ago. On three other greens, we found drains that were plugged with roots from surrounding trees, and some of the greens located beside ponds had the drainage tile entering the pond underwater, causing backup of the harmful gases unable to vent out of the end of the tile. Since we encountered various problems during the installation of the vents, we now refer to them as the “observation ports.” During heavy winter rains, it is reassuring to visually inspect your drains and see the water pouring out of them.
Venting your greens: the process
On most of our greens, the venting process took approximately two days per green; we installed three to four cleanouts and set up two to three exit vents.
Watching the greens change
Since the golf course was built, we have experienced varying degrees of black layer in some of our greens, which we had attributed to the sand used during construction. However, after learning that the lack of venting was preventing the greens’ drainage from functioning properly, we expect the addition of the venting system to improve the condition of the greens.
Irrigating with oxygenated water: the next step for Cordova Bay GC
Water in many soils contains small but significant quantities of dissolved oxygen. When all the soil pores are filled with water, soil microorganisms can extract most of the oxygen dissolved in the water for metabolic purposes, but this small amount is used up quickly. I am sure many processes take place in the soil during a nice steady rainfall, and I have always wondered why plants and turf seem to respond so well to rainfall in comparison to the irrigation cycles we implement throughout the season. I believe one of the processes that occurs is an oxygenation of the soil because of the fairly high count of dissolved oxygen in the rainwater.
In an effort to promote oxygen in our root zones at Cordova Bay, we have installed a Sea Air system. This system has been installed in our pumphouse, and it treats the water by injecting dissolved oxygen into the wet well before the water is pumped onto the golf course. During the peak irrigation period from June to September, the dissolved oxygen level in our wet well is about 6 ppm. With the installation of the Sea Air system, we are now irrigating the golf course with water treated to 15-20 ppm. Although it’s too early to monitor the results, we believe this system will bring us one step closer to promoting a healthy aerobic soil profile while managing quality turf.
By discussing programs that can affect the level of oxygen in the soil profile, I am trying to emphasize the important role oxygen plays in healthy turf. I hope that following this advice will make your greens — and your budget — easier to manage.
References
Brady, N.C., and R.R. Weil. 1999. The Nature and Properties of Soils. 12th edition. Prentice Hall, Upper Saddle River, N.J.
Leo Feser Award candidate
This article is eligible for the 2007 Leo Feser Award, presented annually since 1977 to the author of the best superintendent-written article published in GCM during the previous year. Superintendents receive a $300 stipend for articles. Feser Award winners receive an all-expenses-paid trip to the Golf Industry Show, where they are recognized. They also have their names engraved on a plaque permanently displayed at GCSAA headquarters.
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